Abstract: Tests have been made on the fingerlings of the Cyprinid, Hypophthalmiohthys molitric,to determine the acute toxicity of certain phenolic effluent. The 24-hr TLm. and 48-hr TLm.were found to be 7.75 mg/L and 6.10 mg/L respectively at 6-8℃, and from which a "harm-less concentration" of 1.13 mg/L was computed after the formula of Hart et al. Oxygen con-sumption of the fish remained practically the same in a medium of 3.52 mg/L as in the bl-ank test; marked increase occurred when the concentration of the test solution was raised to6.07 mg/L. On the other hand, concentration up to 1.58 mg/L was sufficient to clicit an avo-iding reaction on the part of the fish. Growth rate of another Cyprinid, Ctenopharyngodonidella, was adversely affected even at a concentration of 0.05 mg/L. In view of these find-ings the authors propose that in evaluating the disposal index of phenolic wastes routine bio-assay method alone seems inadequate and should be supplemented by more refined toxicolog-ical research methods.